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Fig. 1. Tanzania map showing study sites and the distribution of spatially-rarefied occurrence data for Marula tree (Sclerocarya birrea) subsp. birrea (green), subsp. caffra (red) and subsp. multifoliata (pink) in Tanzania.

Table 1. The contribution of environmental factors that define the ecological niches of the Marula tree (Sclerocarya birrea) subspecies in Tanzania under the current environmental conditions.
Subspecies Code Environmental variables Percent
contribution 		Cumulative
contribution 		Permutation importance
(a) Subsp. caffra Bio14 Precipitation of Driest Month 47.0 47.0 3.2
ELV Elevation 20.5 67.5 31.7
CLY Clay soil fraction 11.4 78.9 23.8
SLT Silt soil fraction 9.7 88.6 4.4
Bio19 Precipitation of Coldest Quarter 4.3 92.9 10.1
Bio08 Mean Temperature of Wettest Quarter 3.6 96.5 9.9
SLP Slope 0.7 97.2 6.5
ELC Soil electrical conductivity 0.7 97.9 6.1
ASP Aspect 0.7 98.6 2.5
Bio18 Precipitation of Warmest Quarter 0.5 99.1 0.5
AWC Available water holding capacity 0.4 99.5 0.0
Bio01 Annual Mean Temperature 0.3 99.8 0.4
pH Soil pH 0.1 99.9 0.9
(b) Subsp.
multifoliata		 Bio19 Precipitation of Coldest Quarter 38.6 38.6 5.3
Bio12 Annual Precipitation 16.1 54.7 27.3
PET Potential Evapotranspiration 13.2 67.9 39.9
SOC Soil organic carbon concentration 10.8 78.7 0.3
Bio15 Precipitation Seasonality 10.4 89.1 14
CLY Clay soil fraction 4.0 93.1 2.6
Bio18 Precipitation of Warmest Quarter 3.0 96.1 4.0
SLP Slope 2.5 98.6 3.0
ASP Aspect 0.9 99.5 0.0
Bio07 Temperature Annual Range 0.3 99.8 1.3
ELC Soil electrical conductivity 0.1 99.9 1.6
(c) Subsp. birrea CEC Soil cation exchange capacity 47.2 47.2 3.7
Bio14 Precipitation of Driest Month 16.9 64.1 32.7
SLP Slope 8.9 73.0 39.8
PET Potential evapotranspiration 6.3 79.3 0.5
Bio18 Precipitation of Warmest Quarter 5.3 84.6 17.4
Bio19 Precipitation of Coldest Quarter 4.6 89.2 3.6
pH Soil pH 4.5 93.7 0.0
SOC Soil organic carbon concentration 3.9 97.6 0.5
SLT Silt soil fraction 2.2 99.8 1.6
ASP Aspect 0.1 99.9 0.2
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Fig. 2. Ecological Niches of Marula tree (Sclerocarya birrea) subsp. caffra in Tanzania: (a) ecological niche under the current environmental conditions, (b) ecological niche-protected areas network overlap under the current environmental conditions and, (c)–(f) are ecological niches under RCP4.5 and RCP8.5 for the years 2050 and 2080 predicted by using CCSM4 model. Note: “RCP” is representative concentration pathway and “CCSM4” is Community Climate System Model version 4.

Table 2. Ecological niches of Marula tree (Sclerocarya birrea) (a) subsp. caffra (b) subsp. multifoliata and (c)subsp. birrea in Tanzania under the current environmental conditions and future climates as predicted by CCSM4 and HadGEM2-ES models under RCP4.5 and RCP8.5 for the year 2050 and 2080. Note: “RCP” is representative concentration pathway; “CCSM4” is Community Climate System Model version 4, and “HadGEM2-ES” is Hadley Centre Global Environmental Model 2-Earth System.
Subspecies name Ecological niche class of suitability Area (km2) under the current climate Area (km2) under RCP4.5 Area (km2) under RCP8.5
CCSM4 HadGEM2-ES CCSM4 HadGEM2-ES
2050 2080 2050 2080 2050 2080 2050 2080
(a) Subsp. caffra Not suitable 694 327 708 571 701 428 705 702 696 233 724 908 695 131 709 449 695 147
Moderately suitable 114 307 103 717 105 710 106 031 114 073 110 633 116 027 102 684 112 284
Suitable 62 368 57 890 64 397 58 913 60 838 59 531 60 179 57 830 64 125
Highly suitable 8140 8963 7605 8495 7998 9123 7804 9177 7584
Total suitable area 184 814 170 570 177 713 173 438 182 908 179 287 184 009 169 691 183 994
Protected areas 58 306 53 419 56 573 54 965 59 303 54 497 59 245 53 393 59 335
Other land uses 126 508 117 151 121 139 118 473 123 605 124 790 124 764 116 299 124 658
(b) Subsp. multifoliata Not suitable 757 251 763 077 768 075 762 276 762 870 769 740 769 613 769 225 770 232
Moderately suitable 98 726 95 129 88 563 94 965 94 413 90 310 89 795 89 443 90 048
Suitable 35 303 33 099 34 024 33 865 33 706 30 678 32 200 31 683 30 657
Highly suitable 5889 5865 6507 6063 6180 6441 5561 6819 6232
Total suitable area 139 918 134 093 129 094 134 894 134 299 127 429 127 556 127 945 126 937
Protected areas 47 566 44 413 41 849 47 074 46 285 41 832 41 660 44 990 42 943
Other land uses 92 352 89 680 87 246 87 819 88 014 85 597 85 897 82 955 83 994
(c) Subsp. birrea Not suitable 851 201 868 169 863 270 863 902 862 936 864 283 861 796 863 310 863 379
Moderately suitable 23 749 24 150 13 333 12 649 13 448 12 440 14 510 13 283 13 432
Suitable 4024 4137 2500 2544 2675 2372 2783 2520 2293
Highly suitable 672 713 544 552 588 551 557 534 543
Total suitable area 28 446 29 000 16 377 15 745 16 711 15 364 17 851 16 337 16 268
Protected areas 14 550 14 532 9439 8794 9408 8264 10 237 9124 8601
Other land uses 13 895 14 468 6937 6950 7303 7100 7614 7213 7667
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Fig. 3. Future Ecological Niches of Marula tree (Sclerocarya birrea) subsp. caffra in Tanzania under RCP4.5 and RCP8.5 for the years 2050 and 2080 predicted by using HadGEM2-ES model. Note: “RCP” is representative concentration pathway and “HadGEM2-ES” is Hadley Centre Global Environmental Model 2-Earth System.

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Fig. 4. Ecological Niches of Marula tree (Sclerocarya birrea) subsp. multifoliata in Tanzania: (a) ecological niche under the current environmental conditions, (b) ecological niche-protected areas network overlap under the current environmental conditions and, (c)–(f) are ecological niches under RCP4.5 and RCP8.5 for the years 2050 and 2080 predicted by using CCSM4 model. Note: “RCP” is representative concentration pathway and “CCSM4” is Community Climate System Model version 4.

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Fig. 5. Future Ecological Niche of Marula tree (Sclerocarya birrea) subsp. multifoliata in Tanzania under RCP4.5 and RCP8.5 for the years 2050 and 2080 predicted by using HadGEM2-ES model. Note: “RCP” is representative concentration pathway and “HadGEM2-ES” is Hadley Centre Global Environmental Model 2-Earth System.

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Fig. 6. Ecological Niches of Marula tree (Sclerocarya birrea) subsp. birrea in Tanzania: (a) ecological niche under the current environmental conditions, (b) ecological niche-protected areas network overlap under the current environmental conditions and, (c)–(f) are ecological niches under RCP4.5 and RCP8.5 for the years 2050 and 2080 predicted by using CCSM4 model. Note: “RCP” is representative concentration pathway and “CCSM4” is Community Climate System Model version 4.

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Fig. 7. Future Ecological Niche of Marula tree (Sclerocarya birrea) subsp. birrea in Tanzania under RCP4.5 and RCP8.5 for the years 2050 and 2080 predicted by using HadGEM2-ES model. Note: “RCP” is representative concentration pathway and “HadGEM2-ES” is Hadley Centre Global Environmental Model 2-Earth System.

Table 3. Mean Area Change in km2 of ecological niches of Marula tree (Sclerocarya birrea) (a) subsp. caffra (b) subsp. multifoliata and (c) subsp. birrea in Tanzania under future climates as predicted by CCSM4 and HadGEM2-ES models under RCP4.5 and RCP8.5 for the years 2050 and 2080. Note: “RCP” is a representative concentration pathway; “CCSM4” is Community Climate System Model version 4; “HadGEM2-ES” is Hadley Centre Global Environmental Model 2-Earth System; figures with “–” sign indicate a decrease/negative change and that with “+” indicates an increase/positive change in predicted mean area, and “%” implies mean area change in percentage.
Subspecies name Ecological niche
suitability class 		RCP4.5 RCP8.5
2050 2080 2050 2080
Area change % Area change % Area change % Area change %
(a) Subsp. caffra Not suitable +12 810 +1.8 +4504 +0.6 +22 852 +3.3 +813 +0.1
Moderately suitable –9432 –8.3 –4415 –3.9 –7648 –6.7 –151 –0.1
Suitable –3967 –6.4 +250 +0.4 –3687 –5.9 –216 –0.3
Highly suitable +589 +7.2 –338 –4.2 +1011 +12.4 –446 –5.5
Total suitable area –12 810 –6.9 –4504 –2.4 –10 325 –5.6 –813 –0.4
Protected areas –4114 –7.1 –367 –0.6 –4361 –7.5 +985 +1.7
Other land uses –8696 –6.9 –4136 –3.3 –5964 –4.7 –1797 –1.4
(b) Subsp. multifoliata Not suitable +5425 +0.7 +5722 +0.8 +12 231 +1.6 +12 671 +1.7
Moderately suitable –3679 –3.7 –3955 –4.0 –8849 –9.0 –8804 –8.9
Suitable –1821 –5.2 –1900 –5.4 –4122 –11.7 –3875 –11.0
Highly suitable +75 +1.3 +133 +2.3 +741 +12.6 +7 +0.1
Total suitable area –5425 –3.9 –5722 –4.1 –12 231 –8.7 –12 671 –9.1
Protected areas –1822 –3.8 –3499 –7.4 –4155 –8.7 –5265 –11.1
Other land uses –3602 –3.9 –4722 –5.1 –8076 –8.7 –7407 –8.0
(c) Subsp. birrea Not suitable +14 835 +1.7 +11 902 +1.4 +12 595 +1.5 +11 386 +1.3
Moderately suitable –5350 –22.5 –10 359 –43.6 –10 888 –45.8 –9778 –41.2
Suitable –684 –17.0 –1437 –35.7 –1578 –39.2 –1486 –36.9
Highly suitable –39 –5.8 –106 –15.7 –130 –19.3 –122 –18.1
Total suitable area –6073 –21.4 –11 902 –41.8 –12 595 –44.3 –11 386 –40.0
Protected areas –2887 –19.8 –5126 –35.2 –5856 –40.2 –5131 –35.3
Other land uses –3186 –22.9 –6775 –48.8 –6739 –48.5 –6255 –45.0